The Marcus G. Langseth set out for New York Harbor at 6 a.m. Tuesday, before its voyage had even received the final go-ahead.

Its mission, to use sound waves to record 3-D images deep below the sea floor 15 miles off Long Beach Island, has proved controversial — pitting different factions of the environmental community against each other.

On one side are geologists with the backing of the National Science Foundation who hope the prehistoric past will provide a glimpse into how sea-level rise will affect New Jersey in the future. The other is a bipartisan federation of environmentalists, fishermen and politicians worried about the impact that research could have on present-day sea life and the industries that rely on it.

Aboard the Langseth, Greg Mountain and a team of about 55 beat the tide this morning out of Hell’s Gate and set anchor, despite having no assurance that the National Oceanic and Atmospheric Administration would allow the monthlong expedition to continue any further.

“We had no influence over the process other than what’s happened over the last six months, but the word finally came after a tense bit of time waiting,” Mountain said Tuesday as the vessel continued south.

By 10 a.m., when many who oppose Mountain’s work — including the state Department of Environmental Protection — learned the permit had been issued, the ship had already sailed.

“This is a terrible decision,” Jeff Tittel, director of the New Jersey Sierra Club, said in a written statement about noon. “It is wrong for our coast because it will hurt our environment and marine animals.”

A short time later, DEP spokesman Larry Ragonese said the state was actively appealing NOAA’s decision, arguing the research should be stopped at least during the summer.

“We’re engaging in dialogue,” he said. “We don’t have a lot of time on this, so apparently we need to get moving ... and press them on this as soon as possible.”

At 3 p.m., as the Langseth sailed toward the mouth of Raritan Bay, U.S. Rep. Frank LoBiondo, R-2nd, said it was “unacceptable” for the project to move forward over the objections of New Jersey residents. He has been quietly lobbying against the testing for months.

“There are legitimate questions unanswered about the impact to local marine life, the potential damage to endangered species and habitats, and the need to do such research at this time in the first place,” LoBiondo said.

Mountain and his team plan to use an array of four air guns to send a sonic pulse that will penetrate 2.5 miles — or about 65 million years worth of sediment — into the sea floor in an area they believe will provide a clear glimpse into how sea-level rise has shaped New Jersey’s shoreline. The echo of that pulse will be recorded on computer hard drives on board the Langseth. Fourteen terabytes worth of data will eventually give researchers a 3-D image of what lies beneath the surface.

The plan has drawn controversy due to the potential impact blasting 250 decibels into the water could have on the physical health of endangered marine mammals and the migration patterns of local fisheries. Some have argued the project also could affect any divers who happen to be near the blast when it goes off.

The state, which asked to review the project under the Coastal Zone Management Act, estimates commercial fishing contributes about $1 billion annually to the local economy.

NOAA officials, however, said there will be safeguards in place to protect marine life.

Spokeswoman Connie Barclay said five observers will be watching and listening — with a hydrophone — for marine mammals and any other protected species. Testing must halt if those species come within a prescribed distance of the air guns, she said.

That stipulation is designed to eliminate any behavioral disturbances, Barclay said, which include forcing the animal to move to a different location, stop feeding or swim at increased speed.

“NOAA Fisheries' role is always to ensure we minimize impacts to marine life,” she said.

Barclay said no critical habitat will be included in the testing. The permit ends Aug. 17.

At 5 p.m. Tuesday, Mountain was watching as the Verrazano–Narrows Bridge shrank on the horizon. Speaking over the static of his fading cellphone signal, he said the vessel would arrive at the testing site within eight hours and, after some prep time, begin using the air guns this weekend.

“We’re not here to injure anything,” he said. “We have observers who are continually monitoring the hydrophone array or standing watch 24/7 for any (marine mammal) activity.”

Over the next 34 days, Mountain said the Langseth will sweep back and forth across the testing area. Each pass takes about 6.5 hours, with another 1.5 hours to turn the vessel around and prepare for another pass. The vessel will stay at sea, barring some emergency or possible legal hurdle, for more than a month.

He said this is the first time — Mountain has been involved in four similar studies off New Jersey — the technology has allowed researchers a 3-D view of what’s beneath the surface.

“If things go properly, the research community has an opportunity to examine how sea level impacts coastline anywhere in the world,” he said.

But opponents vow to continue fighting the seismic testing, even as the Langseth nears its destination. Representatives from the various environmental and trade groups, as well as the state, will present information this evening during a public meeting in Barnegat Light.

“The fight’s not over, and there are specific legal issues we’re looking at,” said Cindy Zipf, executive director of Clean Ocean Action, the organization that helped organize the meeting. “I cannot fathom how they’re allowing this to go forward when they’re putting at risk the livelihoods of thousands of New Jersey citizens.”

Contact Wallace McKelvey:

609-272-7256

@wjmckelvey on Twitter

If you go

WHAT: Seismic testing emergency meeting

WHEN: Wednesday, 5 p.m.

WHERE: Barnegat Fire Hall, 10 W. 10th St., Barnegat Light, N.J.